Abstract

Tyrosine kinase 2 (Tyk2), a member of the JAK family, is involved in IL-12- and IL-23-mediated signaling. In the present study, we examined the roles of Tyk2 in the development of myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) by using Tyk2 knockout (KO) mice. In vitro differentiation of Th1 but not Th17 cells was severely impaired in Tyk2 KO CD4 T cells, although Tyk2 KO Th17 cells did not respond to IL-23. Tyk2 KO mice showed complete resistance against EAE with no infiltration of CD4 T cells in the spinal cord. Surprisingly, the number of MOG-specific Th17 cells in the periphery was comparable between KO and wild-type (WT) mice, whereas Th1 cells were greatly reduced in Tyk2 KO mice. Adoptive transfer of MOG-primed WT T cells induced EAE in Tyk2 KO recipients, indicating that Tyk2 in the environment was dispensable for the infiltration of effector T cells into the spinal cord. A reduced but significant number of Tyk2 KO T cells were detected in the spinal cord of mice with EAE, which had been reconstituted with bone marrow cells of WT and KO mice. Furthermore, MOG-immunized Tyk2 KO mice developed EAE after adoptive transfer of MOG-primed WT Th1 cells, which might trigger local inflammation that recruits Th17 cells. Taken together, these results indicate that Tyk2 is critically involved in the pathogenic CD4 T cell responses and thus could be a target molecule for the treatment of autoimmune diseases.

Footnotes

↵1 This work was supported in part by a grant from the Japan Rheumatism Foundation, a Grant-in-Aid for Scientific Research from the Japan Society for Promotion of Science, and by the Program of Founding Research Centers for Emerging and Reemerging Infectious Diseases launched as a project commissioned by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.